Why can't I add bundle to cart?
There are mainly 2 reasons:
1. Draft product
Just like your products, Draft products are not allowed to put in the cart. If you are testing, you have to change the bundle to 'active' status.
After that, the 'Add Bundle to Cart' button will be enabled
2. Protected by password mode
If your store is protected by password mode, you can place a test order with Shopify Bogus Gateway.